The invention concerns a tire with radial carcass reinforcement intended for fitting to heavy building site vehicles and/or off-the-road vehicles such as loaders, trucks, graders or scrapers.
The above tire comprises at least, and mainly, a carcass reinforcement of radial metallic cables and, between the said carcass reinforcement and the tread, a crown reinforcement which comprises mainly an armature, referred to as the working armature, composed of at least two plies of inextensible metallic cables, which are parallel to one another in each ply and crossed from one ply to the next, making angles that may be between 0° and 45° relative to the circumferential direction. The use of machinery fitted with such tires also requires that, radially outside the working plies, there should be an additional armature known as the protection armature, consisting of at least one ply of elastic metallic cables. A cable is said to be elastic if, under a tensile force equal to its breaking load, its relative elongation is at least 3%, while a cable said to be inextensible has a relative elongation at most equal to 0.2% under a tensile force equal to 10% of its breaking load. The cables of the protection ply or plies make angles that may be between 5° and 35° relative to the circumferential direction, and when there are two plies, these are generally crossed over from one ply to the next.
Although initially and as their name implies the primary function of the said protection plies was to protect the working reinforcement against the harsh action of the ground upon the tire, their structural characteristics in contemporary tires result on the one hand in a large contribution towards resistance to separation between the two working plies, while on the other hand, since the life of off-the-road tires is longer, they are insufficient to ensure constant protection during the said life.
A tire of the type considered is subjected by the ground over which it rolls to a great deal of aggression, particularly in the case of heavy loading and transport vehicles. Such aggression by angular, sharp and other objects leads:                (a) to cuts in the tread, which increase the rate of its disintegration, to cutting of the protection plies which then contribute less effectively or not at all towards the resistance to separation between the working plies, and also to cuts in the working plies, with the possibility of spreading and oxidation of the metallic elements in the said plies by humidity and soil particles,        (b) to puncturing of the crown as a whole, while the carcass reinforcement itself may also be punctured depending on the nature and shape of the aggressive object.        
The resistance of the protection plies to cutting and the resistance of the crown to puncturing must be improved.
From U.S. Pat. No. 3,589,125 it is known, in the case of the tread of an aircraft tire comprising a carcass reinforcement formed of several plies of textile elements crossed from one ply to the next, to arrange from one edge of the tread to the other edge on the one hand plies of oblique textile cords flush with the bottoms of circumferential grooves of the tread in order to oppose the effects of centrifugal force on the said tread, and on the other hand two plies of hyper-elastic metallic cables with a relative elongation between 15 and 40%, the said cables being crossed from one ply to the next and the said plies being embedded between the bottom of the tread grooves and the carcass reinforcement of the said tire.
To avoid the initiation and minimize the spreading towards the tread reinforcement of breaks at the bottom of the transverse grooves of an off-the-road tire, French Patent No. 2,388,685 (corresponding to U.S. Pat. No. 4,194,548) proposes the arrangement, in the ungrooved portion between the bottoms of grooves and the crown reinforcement, of at least one ply of cables with low extensibility (steel cables with a relative elongation smaller than 0.5% under a tensile force equal to 10% of the breaking load), the inclination of the said cables relative to the circumferential direction being less than 300 and preferably between 12 and 24°, and the radial distance between the groove bottoms and the said ply of cables being less than but close to one-third of the radial distance between the groove bottoms and the crown ply nearest the tread. Such a structure does not protect against cuts and their spreading, and has a very adverse effect on the resistance of the tire's crown to the shocks imposed by the rapid aggression of large obstacles.